1. Field of the Invention
The present invention relates to a pressure relief valve, and more particularly to a pressure relief valve fitted to a fluid distribution system to control fluid in pressure in the system.
2. Description of the Related Art
In general, as shown in FIG. 2, a pressure relief valve of a conventional type comprises; an inlet port 32 in direct communication with an upstream-side flow passage 31; and, an outlet port 34 in direct communication with a downstream-side flow passage 33. In the conventional relief valve having the above construction, a relief fluid passage 35 intermediate the inlet port 32 and the outlet port 34 is opened and closed by a valve element 37, which has its peripheral portion supported by a resilient diaphragm 36.
As is clear from FIG. 2, the valve element 37 is always pushed downward by the spring 38 so that the relief fluid passage 35 normally stays closed. However, when a fluid pressure in the inlet port 32 reaches a predetermined set point of fluid pressure, the valve element 7 is pushed upward against a resilient force exerted by the spring 38 so that the relief fluid passage 35 is opened to permit fluid to flow through the inlet port 32, relief fluid passage 35, outlet port 34 and then the downstream-side flow passage 33. When a fluid pressure in the inlet port 32 becomes under the set point of the fluid pressure, the spring 38 forces the valve element 37 to move downward so that the relief fluid passage 35 is closed again and stays closed under the influence of the resilient force exerted by the spring 38.
The conventional relief valve having the above construction has a large surface of its valve element 37 exposed to the fluid pressure, the opening/closing operation of the valve element 37 directly depends on variations of the fluid pressure. Due to this, the conventional relief valve tends to incur the chattering problem. In other words, when chattering occurs, the entire area of the diaphragm 36 covering the relief fluid passage 35 extending from the inlet port 32 to the outlet port 34 is exposed to the variation of fluid pressure to rapidly open and close the valve element 37.
Further, in the conventional relief valve, the diaphragm 36 for supporting the valve element 37 keeps its form unchanged until the fluid pressure in the inlet port 32 reaches the set point. When once the fluid pressure in the inlet port 32 reaches the set point, the diaphragm 36 rapidly deforms to open the valve element 37. Consequently, this incurs the chattering problem of the valve element 37 of the conventional relief valve. Further, when chattering occurs, a large force is applied to the valve element 37 to often deform the diaphragm 36 laterally, which increases lateral vibrations of the valve element 37 in chattering. Such lateral vibrations of the valve element 37 prevents the valve element 37 from performing its smooth opening/closing operation. Further, due to the presence of the chattering problem, the conventional relief valve is poor in durability, particularly in its diaphragm 36.